THE TURBULENT STRUCTURE AND SEASONAL VARIATION OF NOCTURNAL COLD DRAINAGE FLOW INTRUDING A PLAIN AND COASTAL AREA.

对1997年4月26日夜间降水冷流的观测分析，揭示了高知平原发生陆风的重力流特征。通过实测可知，排水冷流深度约为75 ~ 80m，速度约为3.5m/s。确定了研究冷流特性的三点。1997年4月至今（1998年3月）在离山区较近的Saoka小学进行的观测表明，该地区的湍流特征和季节变化如下：在上坡气流（山谷风）开始前，气温急剧升高，混合比波动较大。这些现象与沿山坡的热对流有关。高知3号日落前后，沿坡面侵入的气团和沿谷底流入平原的气团构成了冷流。从两种热气象因子（无风条件下的气温[T]、混合比[q]）的直方图来看，夏季各模态为24‰(T), 16‰（g/kg），冬季各模态为7‰(T), 3‰（g/kg）。

The observational case study of the nocturnal drainage cold flow on 26 April 1997 shows the characteristics of the gravity current which intduded into land breeze occurred in the Kochi Plain. From the soder measurements the depth and speed of the drainage cold flow is about 75-80m and about 3.5m/s, respectively.The three points for investigating the feature of the cold flow are settled. The observations from April 1997 to the present (March 1998) at Saoka primary school, the points existed nearer the mountainous area, indicate the turbulent characteristics and the seasonal variations as follows :1.the simultaneous abrupt increase of air temperature and large fluctuation of mixing ratio before onset of the upslope flow (valley wind) are found. The phenomena are associated with the thermal convection along the side slope of mountain.2.The cold flows consisted of the air mass intruded along the side slope and along the valley bottom drained into the plain at around the sunset time of Kochi.3.From the histograms of the two thermal meteorogical factors (air temperature [T], mixing ratio [q] in the calm condition), each modes are 24ﾟC in T,16 (g/kg) in q during summer season, and 7ﾟC in T,3 (g/kg) during winter season.